The present invention relates to a power steering apparatus that assists a steering effort of a driver with a fluid pressure, and more particularly to an integral power steering apparatus mainly useful in large vehicles.
Japanese Patent Application Unexamined Publication No. 2005-255001 discloses an integral power steering apparatus including a main pump that is driven by an engine, and a subsidiary pump serving for complementing the main pump. The main pump is driven to supply fluid pressure in an ordinary condition, and the subsidiary pump is driven in a case where malfunction of the main pump occurs. By thus using the two pumps, the integral power steering apparatus can perform steering assist even when the engine is stopped.